Landoll, in U.S. Pat. No. 4,228,277, discloses water-soluble cellulose ether polymers substituted with (a) a methyl, hydroxyethyl or hydroxypropyl radical and (b) a C.sub.10 to C.sub.24 long chain alkyl group (hydrophobe). Landoll, in U.S. Pat. No. 4,352,916, discloses modifying such cellulose ethers with hydrophobes having 6 to 25 carbon atoms.
Landoll does not discuss using hydrophobes of different lengths in combination (mixed hydrophobes) or the advantages thereof. All of the examples shown therein are directed to cellulose ethers modified with chains having a uniform length, except those used in examples 7 to 10 of U.S. Pat. No. 4,228,277 and example 4 of U.S. Pat. No. 4,352,916 wherein epoxides having 20 to 24 carbon atoms were used. Therein, epoxides having 20 to 24 carbon atoms were used because it is difficult and expensive to separate compounds having longer carbon chains.
The cellulose ethers of Landoll are used as thickeners in, among other things, latex paints. The water-solubility and paint rheological properties of these polymers are primarily dictated by the size and amount of the hydrophobe. For instance, a hydroxyethylcellulose derivative having a long alkyl chain hydrophobe (chain length of 12 or more) exhibits very high aqueous viscosity at a much lower alkyl content than its shorter alkyl chain(less than 8 carbon atoms) containing counterparts. However, similar polymers having long alkyl chains become water-insoluble at a lower level of alkyl substitution. This insolubility severely restricts their usefulness in situations where a higher hydrophobe level is best suited to achieve the desired performance properties, as for instance, improved color development and spatter resistance in paint. Hence, there has been a desire to develop cellulose polymers having such hydrophobes that provide enhanced viscosity and desired rheological properties, without being insoluble, in water.
Recently, nonionic cellulose ether polymers having (a) at least one substituent selected from the group consisting of hydroxyethyl, hydroxypropyl and methyl radicals and (b) a 3-alkoxy-2-hydroxypropyl group wherein the alkyl moiety is a straight chain alkyl group having 2 to 24 carbon atoms have been studied. They are described by t'Sas in U.S. patent application No. 07/063,568 (Filed June 17, 1987) now allowed and given U.S. Pat. No. 4,845,207 and Angerer in U.S. patent application No. 07/223,577 (Filed July 25, 1988), now allowed. Polymers comprising short chain groups, e.g., having 2 to 8 carbon atoms, have been found to be useful in building applications. Those containing longer chain groups, i.e., 6 to 24 carbon atoms, have been found to be especially useful in protective coating solutions, e.g., latex paints. These polymers also suffer from the insolubility problem referred to with respect to the polymers of Landoll.
The inventor was the first to study cellulose ethers having two or more hydrophobes of varied length and has discovered the enhanced rheological properties and improved control obtained with such polymers.